What the standard defines
A mechanical fitting and one electrical contact. The shoe is a sliding rail that accepts a foot; in the centre of that rail sits a contact which closes at the moment of exposure and fires whatever is attached. That much is common across makers, and it is the reason a manual flash or a radio trigger from one system works on a body from another.
Nothing else about the fitting is common. The additional contacts that carry metering, head control and mode signalling are laid out by each maker for its own system, published in its own documentation, and not interchangeable. There is no organisation publishing a shared layout.
What it does not promise
No metering. Through-the-lens metering travels on maker-specific contacts. A flash that fits and fires may still be a manual flash on that body.
No sync speed. The limit belongs to the camera’s shutter, not to the shoe or the flash. It is published per body, and it is the figure that decides whether a picture can be taken in daylight with fill.
No output comparison. A guide number and an energy in watt-seconds describe different things — the first depends on the sensitivity and focal length a maker chose as its reference, the second on energy stored in a capacitor. Neither is the light landing on a subject, and neither converts into the other.
No triggering distance. Radio triggers publish a range in metres, measured in conditions each maker chooses. The shoe carries the trigger; it says nothing about how far the signal travels.
What it works with
Flashes and triggers that present a foot, and the stands, softboxes and diffusers that hang off them. Studio units are the exception worth naming: they are fired through a cable or a radio receiver rather than through the shoe, and the figure that matters for them is the one the trigger publishes.
What people ask before they commit
Will any flash fire on any camera?
Through the central contact, generally yes — it is the one part of the fitting that is common, and it does nothing but close a circuit at the moment of exposure. Everything past that is maker-specific: through-the-lens metering, zoom head control and high-speed modes travel on extra contacts whose arrangement differs, and a flash built for one system loses those functions on another even when it fits mechanically.
What does the sync speed actually limit?
The fastest shutter speed at which the whole frame is open at once. Above it, a focal plane shutter exposes the sensor through a moving slit, so a single burst of flash lights only the part of the frame the slit has reached — the rest stays dark. Makers publish the figure for each body, and the flash cannot raise it: only a mode that turns the burst into a longer pulse works past it, and that mode is named and published per system.
Last reviewed 12 September 2026